Edexcel Chemistry Unit 5 Redox Notes

A set of notes modelled on the specification about the Redox section of the Edexcel Unit 5 examination.

HideShow resource information
Preview of Edexcel Chemistry Unit 5 Redox Notes

First 355 words of the document:

Application of redox equilibria
Please Note: These notes are very heavily based on the Edexcel specification and so are probably best for
revision where the user already understands the topic.
oxidation number - the charge an atom would have if the molecule it is in were composed of ions.
redox - a reaction involving the transfer of electrons, where oxidation and reduction occur side by side.
half-equations - equations showing the gain/loss of electrons in either oxidation or reduction.
In simple ions, the oxidation number is simply the charge on the ion:
Na+ , K+, H+ -> oxidation number of +1
S 2-, O2- -> oxidation number of -2
In molecules, the sum of the oxidation numbers is zero.
In complex ions, the sum of the oxidation numbers of its components is the overall charge on the ion.
In elements in their standard states, the oxidation number is zero.
The change in oxidation number can be related to reaction stoichiometry:
number of electrons gained/lost = change in oxidation number x number of atoms changing in oxidation number
You can make a half-equation by making the calculation above, then balancing out the number of oxygen
(and hydrogen) atoms by adding H+ and H2O molecules on either side.
standard electrode potential - the potential difference between a standard hydrogen electrode and the
half-cell in question, when all liquid concentrations at 1 moldm-3, the temperature at 298K and all
gases at 1 atm.
standard hydrogen electrode - a half cell consisting of a platinised platinum electrode dipping into a
solution of H+ ions (i.e. hydrochloric acid) at1moldm-3, as hydrogen gas at 1 atm pressure is bubbled
over the surface at 298K. This standard system is assigned O electrode potential, and all other
standard electrode potentials refer to this system.
o The reason this happens is because we need a reference in order to calculate the potential of a
single half-cell, which will not conduct electricity on its own.

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Ecell = -Eleft half-cell +Eright half-cell
where E is the standard electrode potential
The left half-cell is the one being oxidised, the right one is the one being reduced.
The standard electrode potential of a whole cell is proportional to both lnK and the total entropy
change.…read more

Page 3

Preview of page 3

Here's a taster:

VO3+ + 2H+ <---> VO2+ + 2H2O
Since both vanadium species have +5 oxidation number, this is NOT redox.
This solution can be reduced to different species by different reducing agents:
equation E
VO2+ + 2H+ + e- <--> VO2+ +H2O +1.00
VO2+ + 2H+ + e- <--> V3+ + H2O +0.34
3+ - 2+
V + e <--> V -0.26
Estimating the concentration of a solution of an oxidising agent
-i.e.…read more

Page 4

Preview of page 4

Here's a taster:

Fuel Cells
The internal combustion engine is very inefficient at converting fuel to kinetic energy and also produced
greenhouse gases, therefore fuel cells are better because of the greater conversion of energy.
Hydrogen fuel cells:
Simplest cell, used in space exploration
H2 is fuel.
O2 is the oxidant.
KOH(aq) is the electrolyte.…read more


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »